There will be a new one soon go to http://www.upstarthq.com and watch that space. Although Kanban is only part of the product, it’s actually going to be product development platform for bootstrapping startups. But the Kanban board and backlog features will likely be free.

You guys should checkout the new entrant Swift-Kanban as well, at http://www.swift-kanban.com. You’ll see our creativity and innovation, right from the website. Try it out and let us know what you feel. 🙂

LeanKit Kanban offers the most flexible board editor available – allowing nested vertical lanes and horizontal swimlanes. If you can draw it on a whiteboard, you can model it in LeanKit. And editing is all done in the board so it takes no time at all.

Customizable card colors, configurable icons for class of service, and gravatars for assigned team member(s) make critical work items jump out. Lanes turn red when WIP limits are exceeded.

In June we’ll add board cloning and an iPad app!

Check-out the site for a free trial or completely free account for up to 5 users.

smartQ has features AgileZen does have not: customized ticket fields, separate area for communication on each ticket and flexible user rights (linked to the columns).
Needless to say the custom fields is a killer feature.

Hey. I tried couple of kanban tools but was a bit disappointed because I had to combine couple of tools to get what I want but then the thinks start to develop a little so in my opinion try kanbanize.com and kanbantool.com. The first one is absolutely free and the other is free for 4 users and 2 board as I can remember.
Good luck! 🙂